I've got a Interarms PPK/S .380 that is failing to feed FMJ ammo after firing. I've put over 300 rounds through it and this was my late father's gun so its probably broken in. I'm not limp wristing it. I had 3 failures from 1 mag. Replaced the older mags and same issue. Gun is well lubed and clean, no burrs or rough spots I can find. It ejects fine, seems to feed from the mag fine, but the slide is not moving to fully closed position after firing. Maybe 1/4 to 1/2 inch open. If I tap the slide with my offhand it fires fine. Rounds drop into the chamber just fine by hand. Hornady CD and Fed Hydroshok feeds just fine, but FMJ ball just won't run and I need afforable practice ammo cause frankly I suck atm . Magtech, Speer, and Aguila won't run. I wondering if its the spring, do I need to have the Feed ramp/barrel polished down like S&W did with their PPK run, or if its something I've not thought of.